Certain estuaries, harbors and lakes have been the recipients of contaminants that have resulted from industrial and other societal activities, These contaminants, commonly metals, pesticides, and persistent industrial chemicals, have concentrated in the surface layer of sediments at the bottom of these bodies of water. Even if all continued influx were to stop, these chemicals constitute a bank or reserve that may remain available to diffuse back into the active ecosystems, and exert toxicity in accord with their composition and concentration. They also remain to comprise a more acute threat in the event of sudden disturbance, perhaps during severe storms or dredging operations or even clean-up operations that may substantially disturb and resuspend the sediment.
There are, indeed, significant bodies of water, with significant economic, aesthetic and ecological value, such as Chesapeake Bay, in which the surficial bottom sediments are toxified to the degree that many would consider any attempt to disturb the sediments as unwise, even for the purpose of attempting to remove them. Similarly, the same concerns surround dredging for its various other reasons, such as deepening shipping channels.
The toxified sediments are commonly not thick, being perhaps of the order of 10-100 cm. These thicknesses have been created by the various processes of sedimentation that have historically been active in the water bodies during the period of polluting. Neither thickness nor concentration of toxic components are necessarily uniform throughout the sediments of any body of water, nonetheless, the total volume of such sediments can be very large where the area is large.
Many of these sediments will be fine grained mud, with high organic content and large and reactive surface area on the very small and weathered mineral fragments, and with various coatings and grains of sulfides and oxides. Each of these traits is associated with ease of entrainment and entrapment of various toxic components.
As can be seen by reference to the following U.S. Pat. Nos. 1,388,040; 552,877; 1,995,238; 3,799,349; and, 4,614,458 the prior art has acknowledged and attempted to solve a somewhat similar problem of sedimentary accumulation; however, these prior art solutions are uniformly devoted to gross sediment accumulation in relatively fast flowing bodies of water, such as streams, rivers, canals and the like wherein the current flows generally in a single direction.
It should further be noted that while the prior art solutions are more than adequate for the specific environment in which they are employed, these previously patented remedies are not particularly suitable to the large expanse generally omni-directional current flows encountered in most harbors, bays, estuaries and large lakes.
It should also be noted that virtually all of the aforementioned prior art solutions envision the physical removal of the accumulated sediments from the bottom portion of the trap receptacle via pumping or mechanical dredging apparatus; and while those removal systems may be adequate for a relatively confined body of water the physical cost of installing such a system in larger bodies of water would not only be prohibitive; but would also result in large volume agitation and redistribution of the settled sedimentary deposits; and as a result would be counter productive to the goals of the present invention.
As a consequence of the foregoing situation there has existed a longstanding need among those individuals and agencies concerned with the removal of toxic sediment from large bodies of water for a relatively simple and straightforward method for accumulating, removing and/or isolating toxic sediments from relatively large bodies of water; and, the provision of such a solution is the stated objective of the present invention.